The present invention relates to pull type agricultural implements supported on ground engaging wheels, and more particularly to a wheel locking system for such implements when unhitched and left parked in a field, lot or other storage area.
Many small agricultural implements, such as round balers, are mounted on ground engaging support wheels and are equipped with a towing bar for coupling the implement to a pulling vehicle, such as a tractor. Because of the relatively small weight of the implement and the low maximum speed of the tractor, it is not necessary to provide the implement with a wheel braking system that operates in conjunction with the tractor braking system. The tractor has the necessary braking capability to stop both the tractor and the towed implement during field operation and transport between fields.
However, when the implement is uncoupled from the tractor and left to stand alone in a field or storage lot, it may be necessary to provide means for preventing the implement from rolling on its wheels and moving from its initial location, e.g., when parked on an inclined surface. It is well known in the art to use wedge shaped blocks in front of, and/or behind, one or both of the wheels to prevent a decoupled implement from moving on sloping ground during storage. Even though implements commonly utilize a pivotally mounted jack extending from the tongue to maintain stability during parking, sufficiently inclined storage areas may still give rise to unwanted movement.
It is also known to use a parking lock for securing one or both wheels to the frame of the implement. For example, the parking lock may comprise a pin which can be inserted into an appropriate receiving cavity on the wheel, as illustrated by the apparatus disclosed in GB Patent No. 823,372. A spring is provided for urging the pin into one of the receiving cavities. For unlocking the wheel, a handle affixed to the pin is turned over along a ramp whereby the pin is lifted and pulled out of the cavity against the force of the spring. For locking the wheel, the handle is turned in the other direction, whereupon the spring forces the pin into one of the cavities.
In prior art locks, such as the one disclosed in the ""372 patent, the pin may engage the cavity in such a manner that a substantial force is needed to remove the pin. This may occur under conditions where the implement is parked on a slope or when the towing vehicle maneuvers in a manner that causes the wheels to be stressed. If the pin cannot be removed manually, then the operator must go to the tractor and move the implement in an attempt to relieve the stress. The operator must then dismount from the tractor and return to the implement to manually remove the pin and thereby disengage the lock. This is a time consuming operation, and in some instances must be repeated until the implement is properly maneuvered to a position that relieves the stress.
Another disadvantage of prior art locks, such as the one disclosed in the ""372 patent, occurs under conditions where the pin is not aligned to engage the cavity when the implement is parked. It then becomes necessary to utilize the tractor to move the implement in a rocking manner, i.e., back and forth, to facilitate alignment between the pin and the cavity. If this occurs when the implement is parked on a slope, maneuvering the towing vehicle in this manner could cause undue stress on the wheels, or at the very minimum, it adds difficulty to an already time consuming and arduous task. In some instances the operator must repeatedly get off the tractor to visually inspect the implement until it is properly maneuvered to an alignment position, permitting insertion of the pin into the associated cavity.
Another known parking lock solution employs a system that utilizes a hydraulic or electric actuator to remove the pin. The obvious disadvantage of this type of system is the complexity as well as the relative expense when compared to the base cost of the small implement on which it is being used.
Therefore, an important object of the present invention is to remedy the above problems and provide an agricultural implement equipped with reliable, yet simple and user friendly means for locking and unlocking the wheels of the implement when the implement is parked.
In pursuance of this and other important objects the present invention contemplates a preferred embodiment wherein an improved parking brake is provided for a pull type agricultural implement comprising a main frame, a pair of ground engaging wheels rotatably attached to the main frame for supporting the implement, means for attaching the main frame to a vehicle for towing the implement, and a parking lock operatively associated with the main frame for preventing rotation of one of the wheels, under conditions where said implement is parked, the parking lock comprising a pin moveable between an extended position in which the pin precludes the rotation of the wheel relative to the main frame, and a release position in which the lock member permits rotation of the wheel relative to the main frame. More specifically the improved parking lock contemplates stop means attached to the wheel, which stop means comprise a plurality of radially aligned shoulders mounted in spaced relationship for defining a like plurality of radially receiving cavities for accommodating the pin, resilient means for providing a holding force for urging the pin into a receiving cavity under conditions where it is in the extended position, and camming means for engaging the frame to provide sufficient force to overcome the holding force, whereby the pin is urged out of said extended position to the release position. The holding force of the resilient means is sufficient to hold the pin against any one of said shoulders under conditions where the pin is not aligned with a receiving cavity when the implement is parked.